This research will be done primarily at Christian Medical College, Vellore, India in collaboration with Dr. Gagandeep Kang as an extension of NIH grant PO1 AI05788 (06/15/04-5/31/09). This revised application seeks to extend multidisciplinary approaches to develop new rapid diagnostics and therapeutics to detect, combat and prevent human calicivirus infections by using recently developed methods to determine the importance of human calicivirus infections in a developing country and also evaluate whether human infections can be caused by animal caliciviruses. The lack of diagnostic capability has limited the recognition of caliciviral disease in developing countries, but these viruses are estimated to cause 23 million infections annually in the US, and are likely to be significant pathogens in the developing world. Recent studies in developed countries have shown there is an unprecedented degree of genetic diversity in human calicivirus isolates, particularly in the noroviruses. Understanding whether the great genetic diversity of these viruses is due to evolutionary mechanisms such as genetic drift and recombination between different human viruses, or to introduction of animal viruses into the human population is critical in trying to develop methods to prevent or interrupt transmission of these infections. The focus of this proposal will be on the use of newly developed techniques to identify a broad range of human and bovine caliciviruses in children from 0 to 36 months who were enrolled in a completed birth cohort study in an urban slum area of southern India and in the animals with whom they come in contact. In the first specific aim, serosurveys will be performed using recombinant virus-like particles (VLPs) from different genotypes of human and bovine caliciviruses to determine if humans possess antibodies to human and bovine caliciviruses as well as to determine the age-specific acquisition of such antibodies. In addition, reverse-transcription polymerase chain reaction (RT-PCR) with a range of known human calicivirus strain-specific primers, followed by sequencing will be used to identify and characterize caliciviruses from children. In the second specific aim, bovine viruses will be sought in children and cattle using known and newly designed primers. Finally, the viruses identified will be used to develop virus-like particles based on novel virus isolates and then antisera will be raised to develop new reagents for future studies to detect antigen with faster, more economical assays than RT-PCR. These studies are important because there is limited information of the burden of disease and circulating calicivirus strains in the developing world. Given the ability of these viruses to evolve and spread rapidly across the world, there is an urgent need to investigate their epidemiology and transmission potential in Asia, where animal-human contact is intimate and prolonged. The proposed studies seek to apply new methods to determine the importance of human calicivirus infections in a developing country and to evaluate whether human infections can be caused by animal caliciviruses. Understanding whether the great genetic diversity of the caliciviruses is due to evolutionary mechanisms such as genetic drift and recombination between different human viruses or to introduction of animal viruses into the human population is critical in trying to develop methods to prevent or interrupt transmission of these infections.